The Viral Epidemiology Branch (VEB) has used a variety of approaches to define the nature and magnitude of malignancies associated with HIV-1 and other chronic infections, including analyses of population-based data, prospective cohort studies, and laboratory investigations. We are currently initiating a limited follow-up of 2,480 subjects with CDC-defined AIDS (i.e., <200 CD4+ T-cells/?l) recruited in 1998-99. Nested case-control studies of incident cancers are planned, utilizing the detailed clinical and interview data and banked blood specimens (plasma and cryopreserved PBMC) collected at enrollment. Our two previous cohort studies of HIV-infected hemophilia patients have been incorporated into a larger cohort which includes HIV uninfecteds, whose prospective followup for cancer is just being initiated. These cohorts will be applied to studies of potential risk factors for AIDS-related malignancy, including genetic polymorphisms and/or altered baseline levels of cytokines and other immune factors, chromosomal translocations, EBV and HHV-8 viral loads, antibody titers, and cell mediated immunity, and environmental exposures and medications. We are continuing our studies of EBV infection and immune response as a causative factor in AIDS-related lymphoma, with determinations of viral load, cell-mediated immunity, antibody reactivity, and other immune system parameters. These studies also include examination of host genetic variation in B-cell-stimulatory cytokines. We are also collaborating with the NIDDK to study HHV-8 reactivation in HIV-positive renal allotransplant recipients. In collaboration with the Occupational Epidemiology Branch, we are continuing our investigations of cytokine polymorphisms as risk factors for gastric cancer. In a collaboration with the Veterans' Administration, we are extending our previous mortality followup of hepatitis C seropositive Air Force recruits from the 1950s, with physical examinations and medical record reviews of surviving cohort members. We are also investigating another VA cohort of liver disease patients originally recruited in the 1970s, for which we are assessing effects of baseline hepatitis C viremia and subsequent infection with HIV.